Table I.
Baseline characteristics (data are number (%) or mean (SD)).
| Overall | Type of frozen embryo transfer cycle |
||
|---|---|---|---|
| Modified natural | Artificial | ||
| Treatment allocation | 959 (100%) | 495 (51.6%) | 464 (48.4%) |
| Age at randomization (years) | 33.5 (4.0) | 33.3 (4.0) | 33.8 (4.0) |
| Age at ovum pickup (years) | 32.9 (4.1) | 33.1 (4.1) | 33.1 (4.1) |
| Duration of subfertility (years) | 3.0 (2.3) | 2.9 (2.2) | 3.1 (2.5) |
| Fertility status | |||
| Primary subfertility | 383 (39.9%) | 196 (39.6%) | 191 (41.2%) |
| Parity | |||
| 0 | 555 (57.9%) | 284 (57.4%) | 271 (58.4%) |
| 1 | 353 (36.8%) | 188 (38.0%) | 165 (35.6%) |
| >2 | 51 (5.3%) | 23 (4.6%) | 28 (6.0%) |
| Initial treatment | |||
| IVF | 426 (44.4%) | 231 (46.7%) | 195 (42.0%) |
| IVF–ICSI | 533 (55.6%) | 264 (53.3%) | 269 (58.0%) |
| Outcome initial treatment | |||
| Live birth | 242 (25.2%) | 116 (23.4%) | 127 (27.4%) |
| Number of diagnoses | |||
| One diagnosis | 879 (91.7%) | 452 (91.3%) | 427 (92.0%) |
| Two diagnoses | 80 (8.3%) | 43 (8.7%) | 37 (8.0%) |
| Diagnoses | |||
| Unknown | 211 (20.6%) | 113 (21.3%) | 98 (19.9%) |
| Severe male subfertility | 424 (41.4%) | 216 (40.7%) | 208 (42.2%) |
| Moderate male subfertility | 129 (12.6%) | 55 (10.4%) | 74 (15.0%) |
| Tubal factor | 140 (13.7%) | 79 (14.9%) | 61 (12.4%) |
| Endometriosis Stage 1–2 | 40 (3.9%) | 23 (4.3%) | 17 (3.5%) |
| Endometriosis Stage 3-4 | 24 (2.4%) | 13 (2.5%) | 11 (2.2%) |
| Hormonal factor | 29 (2.8%) | 20 (3.8%) | 9 (1.8%) |
| Cervical factor | 9 (0.9%) | 3 (0.6%) | 6 (1.2%) |
| Other | 17 (1.7%) | 8 (1.5%) | 9 (1.8%) |
| Number of IVF or IVF–ICSI treatment prior study ET | |||
| 0 | 521 (55.2%) | 274 (56.1%) | 247 (54.3%) |
| 1 | 259 (27.5%) | 127 (26.0%) | 132 (29.0%) |
| 2 | 141 (15.0%) | 73 (15.0%) | 68 (14.9%) |
| 3 | 22 (2.3%) | 14 (2.9%) | 8 (1.8%) |
| Number of FET prior to study ET | |||
| 0 | 334 (34.9%) | 184 (37.2%) | 150 (32.5%) |
| 1 | 509 (53.2%) | 255 (51.5%) | 254 (55.1%) |
| 2 | 75 (7.8%) | 35 (7.1%) | 40 (8.7%) |
| >3 | 38 (4.5%) | 21 (4.2%) | 17 (3.7%) |
| Duration of cryopreservation (years) | 0.71 (1.0) | 0.65 (0.90) | 0.76 (1.0) |
| Survival (%) | 72 | 74 | 70 |
| Developmental stage at cryopreservation | |||
| Cleavage stage (Day 3 or 4) | 886 (92.4%) | 454 (91.7%) | 432 (93.1%) |
| Blastocyste stage (Day 5) | 73 (7.6%) | 41 (8.3%) | 32 (6.9%) |
| Number of embryos transferred | 1.0 (0.6) | 1.0 (0.58) | 0.96 (0.61) |
| Embryo quality score | |||
| Good | 348 (40.0%) | 182 (39.0%) | 166 (40.9%) |
| Reasonable | 288 (33.0%) | 158 (33.8%) | 130 (32.0%) |
| Moderate | 196 (22.5%) | 102 (21.8%) | 94 (23.2%) |
| Poor | 41 (4.7%) | 25 (5.4%) | 16 (3.9%) |
| Endometrial thickness (mm) | 9.0 (1.8) | 9.0 (2.0) | 8.9 (1.6) |